This invention is based on and claims priority to Japanese Patent Application No. Hei 11-212826, filed Jul. 27, 1999, the entire contents of which is hereby expressly incorporated by reference.
1. Field of the Invention
This invention relates to an engine control system, and more particularly to an improved engine control system that controls an idle engine speed.
2. Description of Related Art
A typical engine has an air induction system that introduces air to a combustion chamber of the engine. A throttle valve normally controls the amount of the air delivered. The throttle valve is disposed in an air intake passage and is arranged to move between an open position and a closed position. When the throttle valve is in the closed position, generally no air is supplied to the combustion chamber. A typical engine also has an idle passage that bypasses the throttle valve for delivering a nominal amount of air for maintaining an idle speed.
Fuel is delivered to the combustion chamber through a charge forming device (e.g., a carburetor or a fuel injection device). The amount of fuel is normally controlled to be proportional to the air amount. The air and the fuel are mixed to form an air/fuel charge. The air/fuel charge is then fired at a proper ignition timing for combustion in the combustion chamber The ignition timing is normally controlled by a control device so as to be advanced or retarded from an initial timing in response to various engine running conditions.
In some instances, however, a relatively large amount of air can be continuously supplied to the combustion chamber even though the throttle valve is fully closed. Under this condition, the engine speed exceeds a desired idle speed and the engine operates at speed greater than the desired idle speed unless the operator stops the engine. This abnormal condition can occur, for example, if the throttle valve is broken or bent. The same situation can also occur if the ignition timing is inadvertently advanced.
This situation poses a problem with an engine for a marine propulsion unit such as, for example, an outboard motor. The outboard motor includes an engine and a propulsion device such as, for example, a propeller. A forward, neutral, reverse transmission couples them so as to transmit power of the engine to the propeller and also to shift or switchover the rotational direction of the propeller into one of the forward, neutral and reverse operating conditions.
The transmission typically includes a bevel gear train and a clutch mechanism. The bevel gear train comprises a drive gear connected to a driveshaft, which is driven by an output shaft of the engine, and forward and reverse bevel gears both connected to a propeller shaft at an end portion of which the propeller is mounted. The clutch mechanism selectively couples the propeller shaft with the forward or reverse bevel gear. Both of the bevel gears are engaged with the drive gear but are not drivingly connected to the propeller shaft until coupled together by the clutch mechanism. Each bevel gear has fixed dog clutch teeth, while the propeller shaft has moveable dog clutch teeth. The power transmittable connection is completed when the fixed dog clutch teeth and the moveable dog clutch teeth are coupled with each other. The moveable dog clutch teeth are slideably supported on the propeller shaft and can be moved by a shift actuator.
The operator may operate the shift actuator so as to selectively engage the moveable dog clutch teeth with the fixed dog clutch teeth on the forward bevel gear or the reverse bevel gear, or not engage them with each other. When the propeller shaft is coupled with the forward bevel gear through that connection, the propeller rotates in the forward direction. When it is coupled with the reverse bevel gear, the propeller rotates in the reverse direction.
Normally the shift operations are made under a low engine speed condition, i.e., an idle speed, to easy separation of and engagement between the dog clutch teeth. That is, the operator slows down the engine speed first and then operates the shift actuator. If, however, the engine maintains a speed above a desired idle speed, the engine speed will not reduce to the desired idle speed and the shift operation will be extremely difficult. If this problem occurs, the operator will have difficulty docking the associated watercraft at a desired position. Moreover, the operator will have difficulty establishing a forward or reverse drive condition from neutral.
A need therefore exists for an improved engine control system that can release an engine from an abnormal engine speed so that, for example, the operator can operate a shift actuator without overload.
In accordance with one aspect of the present invention, an internal combustion engine comprises a cylinder body defines at least one cylinder bore in which a piston reciprocates to rotate a crankshaft. A cylinder head is affixed to an end of the cylinder body and defines a combustion chamber with the cylinder bore and the piston. An air induction system is arranged to introduce air to the combustion chamber. The air induction system includes a throttle valve movable between an open position and a closed position. The throttle valve regulates air flow through the air induction system. A throttle valve position sensor is arranged to sense the position of the throttle valve. An engine speed sensor is arranged to sense a rotational speed of the crankshaft. A control device is configured to slow down the rotational speed of the crankshaft, based upon a throttle position signal from the throttle valve position sensor and an engine speed signal from the engine speed sensor, when the throttle position signal indicates that the throttle valve is generally at the closed position and the speed signal indicates that the rotational speed of the crankshaft exceeds a preset speed.
In accordance with another aspect of the present invention, a marine propulsion unit comprises an internal combustion engine, a transmission device, and a propulsion device for propelling the propulsion unit. The transmission device is arranged to transmit engine power to the propulsion device. The transmission device is also adapted to establish a forward, neutral and reverse drive condition for the propulsion device. A shift position sensor is arranged to sense the drive condition. The internal combustion engine includes a cylinder body defines at least one cylinder bore in which a piston reciprocates to rotate a crankshaft. A cylinder head is affixed to an end of the cylinder body and defines a combustion chamber with the cylinder bore and the piston. An air induction system is arranged to introduce air to the combustion chamber. The air induction system includes a throttle valve that is movable between an open position and a closed position. The throttle valve regulates air flow through the air induction system. A throttle valve position sensor is arranged to sense the position of the throttle valve. An engine speed sensor is arranged to sense a rotational speed of the crankshaft. A control device is configured to slow down the rotational speed of the crankshaft, based upon a shift position signal from the shift position sensor, a throttle position signal from the throttle valve position sensor and a speed signal from the engine speed sensor, when the shift position signal indicates that the propulsion device is operating under one of the forward and reverse drive conditions, the throttle position signal indicates that the throttle valve is generally in the closed position, and the speed signal indicates that the engine speed exceeds a preset speed.
In accordance with a further aspect of the present invention, a method of controlling an internal combustion engine is provided. The engine has a crankshaft and an air induction system including a throttle valve. The method comprises sensing a position of the throttle valve, sensing a rotational speed of the crankshaft, and slowing down the rotational speed of the crankshaft if the throttle valve is generally placed at a closed position and the rotational speed exceeds a preset speed.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiment which follows.